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GoMountain tunnels are linear structures constructed in inner ground and geological data usually cannot be fully collected in the tunnel design stage. Therefore, standard support patterns are generally used in construction and modified according to measurements on cutting face during excavation.In recent years, the development of auxiliary methods like umbrella method facilitates the construction on severe ground conditions (unconsolidated ground, fracture zone, water inflow, neighboring construction etc.). However, reliable prediction method to the behaviors of ground ahead cutting face has not been established.

In this study, two sites(Rittou Tunnel and Hirayama Tunnel) employing such auxiliary methods for stability of cutting face are depicted. In the future, more and more tunnels will be constructed under critical and severe conditions, such as construction beneath urban area with thin overburden, large cross section and unsymmetrical in-situ stresses. Therefore, applying appropriate tunnel support and auxiliary method is becoming more and more important.

In this study, two sites employing such auxiliary methods for stability of cutting face are depicted. Rittou tunnel has a cross section of 252m

(Plate in full paper)

Characters of a few commonly used auxiliary methods are described as follows:

- Long steel pipe forepiling (L>5m) Preceding displacement in front of cutting surface could be inhibited by placing long steel pipe ahead of cutting surface. Recently, applying this method by general construction instruments in tunnel construction becomes possible. It has advantages in construction period and economy and is adopted increasingly.
- Injection forepoling (L<5m) This method is an extensively adopted forepoling method, which strengthens the necessary region of preceding ground by injection. In large-section cases, this method sometimes cannot inhibit the preceding displacement.

ISRM-SINOROCK-2009-175

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

ahead, auxiliary method, borehole, condition, construction, Drilling, drilling energy, dust collector, estimation, excavation, face, geological condition, ground, ground estimation system, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, study, support, surface, system, tunnel

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.35)

The Punch-Through Shear with Confining Pressure (PTS/CP-) experiment has been proven to be a reliable testing method for the determination of Mode II fracture toughness. The Mode II fracture toughness, K

An alternative to the empirical continuum mechanics strength criteria are fracture mechanics based approaches. Linear fracture mechanics in general assumes preexisting discontinuities in a material that act as stress concentrators. The magnitude of the stress concentration governs the brittle fracture process. If pre-existing cracks or flaws are propagated by the stresses and coalesce to form larger discontinuities, the structures may loose integrity and fail. The mechanistic criteria try to mirror the physical origin of the processes and are therefore more exact.

Based on the principles of fracture mechanics, it is possible to not only asses the stability and safety of underground constructions, like caverns, tunnels or boreholes, but also to simulate – based on physical principles – the development of fractures in the vicinity of such openings. From the simulations the geometry of fracture patterns might be derived and used for different aspects, like fluid flow simulations. Some software packages are already available, e.g. Fracod2D, or under development.

Linear fracture mechanics provides the tools to estimate the stress and displacement fields around the tip of a discontinuity. Cracks or fractures are usually subdivided into three basic types, namely Mode I, Mode II and Mode III, based on the crack surface displacement (Lawn 1993; Fig. 1A). In Mode I, the tensile mode, the crack tip is subject to displacements perpendicular to the crack plane. In Mode II the crack faces move relatively to each other in the crack plane.

ISRM-SINOROCK-2009-141

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

Artificial Intelligence, circle, construction, design, hydraulic fracturing, increase, optimization, Optimization Design, permeability, permeability coefficient, pore, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, rock, settlement, subsea tunnel, support, Thickness, tunnel, Upstream Oil & Gas, water, water inflow, well completion

SPE Disciplines:

The granitoid rocks of Sharm El Sheikh are in south Sinai include alkali feldspar granite. Petrographically, the alkali feldspar granite characterized by the predominance of alkali feldspar, quartz, amphibole, biotite and plagioclase, the secondary minerals are Kaolinite, chlorite and sericite. The hydrothermal solutions are responsible for the formation of muscovite after feldspars and biotite, as well as increasing the cracks in the granite. K-metasomatism changed the physical properties of the granite, increasing their porosity, brittle extent, and providing the storage space for mineralization. Progressive alteration of the rocks has been marked by gradual transformation of the fresh granite to altered rocks. With increasing intensity of alteration, newly formed cracks connect with and intersect preexisting tectonic cracks, providing an isotropic permeability structure for solutions to flow. Polarizing microscope used to elucidate the optical properties and abundance of mica (biotite and muscovite) in the groundmass of granite asserts an important role in the formation of cracks. The influences degree of alteration on the granite consistency is studied numerically with a rock failure process analysis code, RFPA

Collected samples represented the alkaline rocks of G.Al Att, G.Umm Markha, G.Hedmaiah, G.Al.Khoshby and G.Mdsosss

This research aim to study the petrological controls effect on the reduction of mechanical properties, also to gain a better understanding of the influence of the alteration process on the granite failure to apply a numerical model based on mechanics that can be used for analysis.

Alkaline rocks are most briefly defined as igneous rocks carrying feldspathoids and /or alkalis/pyroxene/amphiboles, and having a surplus of alkalis when compared to petrographically related rocks.

The study of alteration effects, on strength and deformational behavior of rock under uniaxial compression environment is of vital necessary; most engineering works are confined to shallow depths where weathering and alteration have a dominant role to play and affects almost all chemical and physical properties of rocks. In this study, the hydrothermal alteration and weathering events in the Sharm El Sheikh granite have been studied, since they caused the most important solution actions through the fractures and cracks that affected the consistency of the rocks.

ISRM-SINOROCK-2009-042

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

alteration, alteration effect, alteration mineral, Artificial Intelligence, Behavior, biotite, compression, crack, failure, Feldspar, flow in porous media, Fluid Dynamics, granite, granitoid rock, hydrothermal, mineral, numerical simulation, process, quartz, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, rock, strength, stress, structural geology, Upstream Oil & Gas

Country:

- Asia (0.69)
- Africa > Middle East > Egypt (0.41)

SPE Disciplines:

- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (0.54)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.49)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.34)

A stress calculation method was proposed for the new stress measurement technique using the borehole slotter device. The 2D borehole slotter is an instrument which is used in HQ boreholes (96-104 mm diameter), and allows calculation of 2D stress tensor in a plane normal to the borehole axis. This instrument enables calculation of in-situ stress tensor using three boreholes without the need for mounting strain gauges on the borehole wall. The borehole slotter technique requires cutting of half moon shaped slots at different orientations parallel to the test hole axis using a small diamond impregnated blade and monitoring of the strains which are relieved normal to the slot direction. The aim of this paper is to evaluate the effects of key test parameters on the slotter test results. A precise 3D numerical model of typical slotter test condition was constructed using the FLAC3D code. The effects of variations in rock mass deformation modulus on the strain/stress relaxation, and thus borehole slotter test results, were investigated numerically. The validity of numerical findings were discussed and compared against practical observations. Accordingly, the borehole slotter tests conducted at Bakhtiari dam site-Iran was simulated numerically. A very good agreement was achieved between numerical and field test results. The obtained numerical results provided valuable insights in selecting the governing in-situ stress condition from the recorded field data.

Since the slotter technique has proven reliable in the field and has had certain commercial successes, attention is paid to improve the accuracy of the calculated stresses by considering complexities such as rock mass behavior and heterogeneities at the measurement point. The main goal of this paper is to demonstrate the mechanisms involved the in-situ stress measurement using the slotter technique. The process of in-situ stress measurements conducted at Bakhtiyari dam-Iran was successfully modeled demonstrating the validity of numerical approach in simulating the process.

(Figure in full paper)

Before, during, and after slotting, the circumferential strain is measured at the borehole wall in the vicinity of slot and the tangential strain is measured by a specially developed recoverable strain sensor (Fig. 1) (Foruria, 1987; Bock, 1984). The strain gauge is mounted at 15 degrees from the slot location according to the INTERFELS test procedure recommendation.

ISRM-SINOROCK-2009-094

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

Bakhtiari dam, borehole, borehole slotter, borehole slotter test, calculation, field, function, in-situ stress, numerical modeling, process, relaxation, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, rock, slotter, strain, stress, test, variation

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)

The paper presents a description of the Picote II site, the objectives of the study that was carried out to assess the in situ state of stress in the rock mass, details of the testing programme and the methodology used for its interpretation. An overcoring testing programme was performed at the design stage, and a specific methodology was developed for the global interpretation of the test results, making use of a numerical model and considering the effect of the existing canyon on the stress field. This enabled to make recommendations regarding the initial stress field to consider in the design of the powerhouse cavern.

Owing to the scarce information obtained at the design stage and to the high values of the calculated horizontal stresses, it was decided to perform additional stress measurement tests, using small flat jacks, once construction started and excavation of the adits reached the proximity of the underground powerhouse. Numerical simulations were also done for its interpretation and they confirmed the stress levels obtained at the design stage. The monitoring scheme implemented in the powerhouse cavern includes instrumentation to measure stress changes, which will occur during the excavation. Finally, the significance of the state of stress assessment to the powerhouse design and to the interpretation of monitoring data collected during construction is discussed.

The designer included in the site investigation tests for determination of the in situ state of stress, to be used as input to the numerical models of the underground structures. At the design stage, six STT (strain tensor tube) overcoring tests were carried out in 2 boreholes. A specific methodology was used for global analysis of the test results, in order to obtain the most likely stress field.

Owing to the relatively scarce information obtained at the design phase and to the high horizontal stresses that were determined, the designer decided to perform additional stress measurement tests, using small flat jacks, once construction started and excavation of the adits reached the proximity of the underground powerhouse. Having in mind the influence of high in situ stresses on the behaviour of the powerhouse cavern, STT cells were also included in its monitoring scheme.

ISRM-SINOROCK-2009-043

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

cavern, design, excavation, Horizontal, horizontal stress, interpretation, location, Picote, picote ii underground, powerhouse, powerhouse cavern, powerhouse design, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, rock mass, situ state, State, stress, stress assessment, test

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)

Wang, C.H. (Institute of Crustal Dynamics) | Guo, Q.L. (Institute of Crustal Dynamics) | Yang, S.X. (Institute of Crustal Dynamics) | Ding, L.F. (Institute of Crustal Dynamics) | Hou, Y.H. (Institute of Crustal Dynamics)

Building the underground water-sealed petroleum storage cavern is one important access to assure safe and stable national petroleum storage system. Considering these reasons, some national departments are planning to build one large-scale strategic petroleum storage project in Bohai Gulf. For the special underground structure features, magnitudes and orientation of far-field stresses of planned project area shall be studied in detail. The hydrofracturing measurements has been done in five boreholes of about 140m deep; for the scattered measurement results, it is hard to find out the intrinsic relationships between different measurement spots; therefore, the Shoerey’s Model is taken to process all the measurements, and then the magnitude of stresses at the cavern section is determined accurately; the maximum horizontal stress is 11.02±1.0MPa, and minimum horizontal stress is 6.82±1.0MPa; the orientation of maximum horizontal stress is 76°(±13°), which coincides with the findings by B. C. Haimson, et al. in Korea and the data from WSM, i.e., the orientation of far-field stresses in this region should be between WSW-ENE and E-W. The far-field stresses have few effects on the stability of underground structure according to the stress-to-strength ratio method proposed by Hoek E.; during the excavation, the linear elastic response is the major phenomenon in intact wall rock mass, but falling or sliding of blocks and wedges may occur in some local parts.

ISRM-SINOROCK-2009-059

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

borehole, calculation, cavern, discontinuity, Downstream Oil & Gas, Engineering, far-field stress, granite, Horizontal, in-situ stress, layer, moderately weathered, MPa, natural gas storage, orientation, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, rock, stress, Tab, underground petroleum storage cavern, Upstream Oil & Gas

SPE Disciplines:

This paper presents an application of the rock mass classification systems, namely, Geomechanics Classification System (RMR), Geological Strength Index (GSI) and the newly adapted A-RMR for the characterization of the rock masses surrounding the portals of the Ordu Peripheral Highway Tunnel. In order to characterize the rock masses, which mainly consist of flysch (mostly alternation of sandstone, marl and siltstone) and pyroclastics (agglomerate and tuff), engineering geological investigations have been carried out in three stages as surface, subsurface and laboratory investigations along the tunnel route. Sixteen boreholes with a total length of 1497 m have been drilled along the tunnel route to assist and verify rock mass classifications. Approximately, seventy five rock core samples have been obtained for rock mechanics tests. The shear strength and geomechanical properties of the rock masses were assigned as a result of a synthesis of the results of laboratory testing, GSI, RMR and the newly adapted A-RMR methods. The information provided from all investigations has been gathered and handled for the characterization of the rock masses governing the portal slope stability of open-cut excavations of the tunnel. Kinematical and limit equilibrium analyses of the tunnel portals have been employed for portal slope stability considerations.

(Figure in full paper)

Upper Cretaceous aged Mesudiye formation is the oldest lithostratigraphic unit near the project area and its lower bound can not be observed. The inferred thickness of this formation is about 1000 m. Both tunnel alignments will be mostly cut by the Mesudiye formation which is comprised of agglomerate, basic lava flow, limestone, tuffite, mudstone, siltstone and sandstone. The description of this formation was first made by Terlemez and Yõlmaz (1980).

Another formation to be driven by the initial portion of the Boztepe tunnel is Akveren formation which may be correlated to the Fatsa formation of Terlemez and Yõlmaz (1980).

ISRM-SINOROCK-2009-008

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

analysis, classification, discontinuity, Engineering, fly sch, flysch, formation, MPa, portal, portal slope, portal slope stability, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, rock, rock mass, shear strength, stability, strength, structural geology, surface, tunnel, Upstream Oil & Gas

Country:

- Asia > Middle East > Turkey (0.71)
- North America (0.47)

An extensive site investigation program was carried out between 2002 and 2007 to characterise the rock mass at Forsmark Sweden, to assess its potential for hosting a used nuclear fuel repository at a depth between 400 and 700 m. Stress campaigns using both overcoring and hydraulic fracturing, including the hydraulic testing of pre-existing fractures were carried out to establish the in-situ stress state. Using only those measurements that had approximately the same Azimuth, the minimum horizontal stress from the overcoring measurements were compared to the minimum horizontal stress from hydraulic fracturing. The hydraulic testing was carried out using special testing procedures designed to minimise the risk for inducing horizontal fractures or fracture rotation. Despite these efforts the hydraulic fracturing results indicated that the minimum horizontal stress was approximately 50% of the magnitude given by the overcoring measurements and approximately equivalent to the vertical stress. It appears that the prominence of the open subhorizontal fractures at Forsmark combined with high horizontal stresses prevented both the hydraulic fracturing and HPTF from providing reasonable estimates of the minimum horizontal stress. The horizontal stress magnitudes from the overcoring were found to be in agreement with indirect measurements and observations made during the site characterisation program.

As noted by Doe et al. (2006) not all stress measurement methods carried out in deep boreholes will work in all geological environments. They note that in over-stressed rock, e.g., rock masses where the horizontal stresses significantly exceed the weight of the overburden (a thrust regime) none of the stress measurement techniques work particularly well. Because hydraulic fracturing produces a fracture normal to the minimum stress, hydraulic fracturing in such a stress regime tends to produce horizontal fractures and hence measures the weight of the overburden /Evans and Engelder 1989/. The overcoring method relies on elastic theory and in such a stress regime micro-cracking may occur inducing a nonlinear stress-strain response which makes it difficult to interpret the results (Martin and Christiansson 1991).

While it may be difficult to measure the in-situ stress state directly using traditional overcoring and hydraulic methods in some in-situ stress regimes (geological environments), the results from such measurement campaigns, nonetheless, contribute significantly to understanding the in-situ stress state at a site.

ISRM-SINOROCK-2009-039

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

borehole, campaign, Comparison, establish, Forsmark, fracture, fracture domain, fracture frequency, frequency, Horizontal, hydraulic fracturing, hydraulic method, in-situ stress, intermediate principal stress, Magnitude, orientation, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, rock mass, stress, Upstream Oil & Gas, vertical stress, well completion

SPE Disciplines:

The issue of prescribing the support requirements for stratified roofs of no major discontinuities otherthanhorizontalbeddingplanesisherebyapproached ideallyaswellaspragmatically. Firstly, the unreinforced case is analytically defined; the solution acquired by elementary beam theory for a fixed beam under distributed load is compared to an Airy stress function solution for a fixed beam under its own weight based on Timoshenko beam theory. Finally, a finite difference numerical solution is performed and verified. The model is then used to investigate the behavior of a two-member stratified roof with contact plane governed by the angle of friction and tightened inordertomobilizetheshearingreactionforceatthediscontinuity.Parametric analyses to investigatethepossibleeffectsofelasticparameterssuchasthe modulusofelasticityandthe Poisson’s ratio and also the interbedding friction angle and its effect on the response of the model conclude thissection. The last part involves the numerical implementation of a bolting support system providingthe previously determinedforce andthe prescription ofits characteristics,i.e. length,spacing,diameterandpretensionofbolts.The impact of applying concentrated compressive forces instead of the theoretical distributed support is also outlined.

(Equation in full paper)

The maximum stress components σ

The modeled plane strain beam was of L/t=12.5, zero Poisson’s ratio, 1 m length, density 2400 Mg/m

ISRM-SINOROCK-2009-123

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

angle, beam, bolt, deflection, effect, elementary beam theory, equation, friction, plane, Poisson, reinforcement factor, requirement, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, shear, solution, stress, stress function, support, Upstream Oil & Gas

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.49)

Chen, Yifeng (Laboratory of Water Resources and Hydropower Engineering, Wuhan University) | Mao, Xinying (Laboratory of Water Resources and Hydropower Engineering, Wuhan University) | Zhou, Chuangbing (Laboratory of Water Resources and Hydropower Engineering, Wuhan University)

The concrete faced rockfill (CFR) dam of the Shuibuya Hydropower Project, with the maximum height of 233 m, is up to now the highest CFR dam built in the world. During construction and after completion of the project, however, a group of cracks were discovered on the concrete face slabs, which is the major measure for seepage control of the dam. Though measurements have shown that the cracks would not endanger the safety of the dam, sensitivity analysis is still needed to predict the seepage behavior of the dam in partial or complete deficiency of the face slabs on a coupled hydro-mechanical (HM) basis. In this study, a coupled saturated flow and stress process was considered to investigate the effects of the concrete face slab deficiency on the seepage behavior and safety of the dam. The deformation response of the rockfills is described by using the Duncan-Chang nonlinear elastic E-B model, together with the Desai’s thin layer elements for the interface between the face slabs and the buffer material. The coupling effect of stress on hydraulic conductivity of the rockfill is described by the Gangi’s model, which is embedded in the code for saturated flow process formulated with an adaptive variational inequality for eliminating the singularity at the outlet seepage points and resultant mesh dependency.

During construction and after completion of the project, however, a large group of cracks were observed on the concrete face slabs, as shown in Figure 1. Since use of the face slabs is the major measure for seepage control of the dam, the seepage behavior may deteriorate by the cracks. Though field measurements show that the cracks would not endanger the safety of the dam, sensitivity analysis is still needed to predict the seepage behavior, deformation and stability of the dam for partial or complete deficiency of the face slabs, as a coupled hydro- mechanical (HM) process.

In this study, a coupled saturated flow and stress process was established based on Biot’s consolidation theory to examine the effects of the face slab deficiency on mechanical response and seepage behavior of the dam. The Duncan-Chang nonlinear elastic E-B model (Duncan et al. 1970) and Desai’s thin layer elements (Desai et al. 1984) are used to model the deformation characteristics of the rockfills and its interaction with the stiffer concrete face slabs.

ISRM-SINOROCK-2009-076

ISRM International Symposium on Rock Mechanics - SINOROCK 2009

Comparison, complete deficiency, concrete face slab, crack, dam, effect, hm effect, model, process, renewable energy, Reservoir Characterization, reservoir description and dynamics, reservoir geomechanics, Rockfill, seepage, seepage behavior, Shuibuya CFR dam, slab, Upstream Oil & Gas

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.47)

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